1. Field of the Invention
The present invention relates to an isolation film of a semiconductor device and a method for fabricating the same, and more particularly, to an isolation film of a semiconductor device and a method for fabricating the same, which prevent the isolation film from being damaged due to misalignment when forming a contact hole in a region adjacent to the isolation film, to ensure stable effective isolation distance.
2. Discussion of the Related Art
Generally, in an integrated circuit, it is necessary to electrically isolate each device formed in a surface of a semiconductor substrate. In a bipolar device and a metal oxide semiconductor (MOS) device, a field oxide film is thickly formed so as not to cause undesirable short and punchthrough between adjacent devices, or impurity ion is implanted into the semiconductor substrate, in which a field oxide film will be formed, so as not to form a channel and then is diffused into substrate to substantially isolate the devices from one another.
With high packing density of the semiconductor device, methods for reducing the dimensions of a field region for isolation of devices and an active region for the formation of devices have been proposed. In general, local oxidation of silicon (LOCOS) process has been widely used in a method for forming a field region for isolation of devices due to its simple process steps and excellent reproduction.
A conventional method for forming an isolation film of a semiconductor device will be described with reference to the accompanying drawings.
FIGS. 1a to 1e are sectional views illustrating a conventional method for forming an isolation film of a semiconductor device.
As shown in Fig. 1a, an oxide film 2 and a nitride film 3 are sequentially formed on a semiconductor substrate 1. Subsequently, a field region F and an active region A are defined. The nitride film 3 and the oxide film 2 are then selectively patterned by photolithography and etching processes to expose the semiconductor substrate 1 in the field region F.
As shown in Fig. 1b, the exposed semiconductor substrate 1 is oxidized by LOCOS process to form a field oxide film 4. At this time, the field oxide film 4 is not formed on the nitride film 3 because oxygen is substantially not diffused into the nitride film 3.
As shown in Fig. 1c, the nitride film 3 and the oxide film 2 over the active region A are removed. Subsequently, a gate electrode (not shown) is formed on the semiconductor substrate 1 in which the active region A is defined. An impurity region 5, which will be used as source and drain, is then formed on the semiconductor substrate 1 at both sides of the gate electrode.
As shown in Fig. 1d, an interlevel oxide film 6 is formed on the entire surface of the impurity region 5 and the field oxide film 4. Subsequently, a contact hole (for example, a node contact hole or a via hole) region is defined and then the interlevel oxide film 6 in the contact hole region is selectively removed to form a contact hole 7. At this time, the field oxide film 4 having the same etching selectivity as the interlevel oxide film 6 is partially etched due to misalignment, which is likely caused by high packing density of the semiconductor device. It is thus noted that the width of the field region F is reduced to F'.
As shown in Fig. 1e, a conductive layer 8 is formed on the entire surface of the interlevel oxide film 6 including the contact hole 7. The conductive layer 8 is then selectively patterned to remain over the contact hole 7 and some portion of the interlevel oxide film 6 adjacent to the contact hole 7.
The conventional method for forming an isolation film of a semiconductor device has several problems.
Since the width of the field region defined before forming the semiconductor device is reduced to F' due to misalignment caused by high packing density of the semiconductor device, final effective isolation distance is shortened, thereby deteriorating reliability of the field region. To solve such a problem, it is necessary to widen the width of the effective isolation distance. However, this is contrary to achieving high packing density of the semiconductor device.